The present invention relates to technique for measuring and inspecting a microfabricated circuit pattern and others using an electron beam.
A scanning electron microscope is an apparatus that focuses a primary electron beam emitted from an electron source by an electromagnetic lens, detects a signal electron such as a secondary electron and a backscattered electron respectively emitted from a specimen in scanning and irradiating the primary electron beam on a surface of the specimen by electromagnetic deflection, and acquires an image. As the scanning electron microscope can acquire an image of higher resolution by focusing the primary electron beam, compared with an optical microscope, the scanning electron microscope is applied to semiconductor metrology equipment used for measuring dimensions of a microfabricated circuit pattern in a semiconductor manufacturing process and others. In addition, recently, large field inspection of a pattern formed on a semiconductor wafer becomes more important and inspection equipment that precisely executes the large field inspection is demanded. In the large field inspection of the semiconductor pattern dimensions by the scanning electron microscope, high throughput is required in addition to similar resolution to the semiconductor metrology equipment.
In the semiconductor metrology equipment using the scanning electron microscope, movement of field of view (FOV) by driving stage in XY directions, operation for acquiring an image at a measurement location and measuring dimensions of a pattern are executed sequentially, and this series of operation is repeated. When this operation is applied to large field inspection of the semiconductor pattern, repeating the movement of FOV by the driving the stage causes a bottleneck of throughput. Therefore, if a movement range of FOV by primary electron beam deflection (hereinafter called beam deflection) can be enlarged, a frequency of stage movement can be reduced and throughput can be enhanced.
In the meantime, it is important, so as to precisely measure dimensions of a semiconductor pattern with movement of FOV by primary electron deflection, that detection of signal electron of an image is uniformly acquired in an area of beam deflection. Generally, the scanning electron microscope with high resolution has a through the lens (TTL) detection system in which signal electrons emitted from a specimen is detected after passing through the objective lens. In the TTL detection system, signal electrons are acted refraction by the objective lens and deflection by the deflection field like primary electron beam. As a result, the signal electron collides with an optical component such as a deflector before the signal electrons reach the detector and a detection rate of signal electrons varies depending on beam deflection range. To avoid this situation, a means for controlling a trajectory of signal electrons is required.
For the unit that controls a trajectory of signal electrons, Wien filter is known. In the scanning electron microscope, the Wien filter is generally used for a deflector in which deflection fields of an electrostatic field and a magnetic field are superimposed so as to cancel deflection of the primary electron beam and to deflect only a signal electron. For example, for technique for generating a deflection field that deflects only a signal electron without deflecting a primary electron beam, Japanese Unexamined Patent Application Publication No. 2012-3902 can be given. In Japanese Unexamined Patent Application Publication No. 2012-3902, a deflector used for movement of FOV by beam deflection is configured by Wien filter and a deflection field that deflects only a signal electron without deflecting a primary electron beam in the deflector is superimposed on a deflection field of the primary electron beam.